Since the invention of the integrated circuit (IC), the semiconductor industry has experienced rapid growth due to continuous improvements in the integration density of various electronic components (i.e., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from repeated reductions in minimum feature size, which allows more components to be integrated into a given area. These smaller electronic components also require smaller packages that utilize less area than previous packages. Some smaller types of packages for semiconductor devices include quad flat pack (QFP), pin grid array (PGA), ball grid array (BGA), flip chips (FC), three dimensional integrated circuits (3DIC), wafer level packages (WLP), wafer-level chip scale packages (WLCSP), and package on package (PoP) devices.
In a typical manufacturing process, active and passive devices may be made within a substrate, and connected by interconnect structures such as metal contacts formed on metallization layers and dielectric layers. Contact pads are formed above the metallization layers to make connections to packages. Typically, redistribution layer (RDL) or post-passivation interconnect (PPI) may be used to fan out wires for contact pads, followed by the formation of UBM layers connected to RDLs and solder balls on the UBM layers to establish electrical contacts between contact pads of a chip such as input/output pads and the substrate or lead frame of the package.
Ground-up contact pads can be used for packages such as flip-chip packages. Ground-up contact pads require no redistribution layer, instead UBM layers and solder balls are placed on ground-up contact pads directly, and ground-up contact pads are connected to metal contacts within a plurality of metal layers of the chip. However, conventional interconnects for ground-up contact pads occupy large areas of metal layers, which ultimately limit the areas available on metal layers for other functions such as device routing. Methods and apparatus are needed for reducing metal layer areas occupied by metal contacts under ground-up contact pads, and at the same time, increasing the area available for other purposes such as device routing.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the preferred embodiments and are not necessarily drawn to scale.